Various therapeutic treatments require access to blood flowing through a circulatory system. For example, treatments in the fields of hematology, oncology and/or pharmacology may require direct access to circulating blood. Some treatments, such as dialysis, require an extraction and reintroduction of blood. The blood extracted from the body is filtered, waste products are removed and the filtered and “clean” blood is reintroduced into the circulatory system.
To perform dialysis, it is necessary to have access to the blood. Additionally, the access to the blood should provide a high extraction throughput or flow rate. The flow rate allows a sufficient amount of blood to be extracted within a given period of time. Efficacy of the dialysis procedure may be dependent upon the extraction throughput.
When performing dialysis, one method of accessing the blood is via an intravenous catheter. The catheter may be inserted into a large vein. Large veins, such as the vena cava, jugular vein or femoral vein, allow for a higher extraction throughput than do other veins.
However, a catheter is a foreign body in the vein, and may trigger venous stenosis in the vein wall. The venous stenosis may scar and occlude the vein. As a result of the stenosis and occlusion, multiple access sites must be utilized and a patient on long term dialysis may “run out” of usable veins for catheter access. In addition, a catheter may protrude out of a patient's skin and staving off infection is a common challenge when employing catheter access. However, the patient may desire catheter access because, after insertion, accessing the patient's blood through connection of the catheter to a dialysis machine does not require repeated needle pricks.
Another access method is to surgically form an arteriovenous (“AV”) fistula. To form the fistula, a surgeon joins an artery to a vein, bypassing narrow capillaries. Arteries carry blood away from the heart and blood typically flows faster, and at a higher pressure, through arteries than veins. By transferring directly from an artery to a vein without intervening capillaries, blood flows swiftly from the artery into the vein. A fistula may be formed using an anastomosis, and may take 4-6 weeks to mature.
After maturity, two needles are inserted into the vein distal to the created fistula. A first needle extracts blood which is transferred to a dialysis machine. A second needle receives the filtered blood from the dialysis machine and reintroduces the filtered blood into the vein.
A fistula is characterized by lower infection rates than catheter access. However, because the fistula is always “on” and blood is always flowing through the fistula, the fistula may stimulate a “steal syndrome.” The steal syndrome occurs when insufficient blood flow reaches the bypassed capillaries. Blood may be drawn through the fistula and returned to general circulation through the vein, preventing adequate blood flow to extremities of a limb. The steal syndrome may result in coldness in the extremities and tissue damage if severe.
A fistula may also be associated with development of an aneurysm in the vein. While undergoing dialysis, needles must be regularly inserted into veins distal to the fistula to extract and return blood. The regular needle insertions may weaken a wall of the vein, increasing a likelihood of an aneurysm.
Another dialysis access method is to create an AV graft. The graft operates under principles similar to the fistula. The graft creates an artificial conduit that transfers blood flow from an artery directly into a vein. Unlike the fistula, the graft joins the artery and vein using a synthetic material. A graft typically matures faster than a fistula, and may be used in cases where a patient's anatomy is not optimal for creation of a fistula. The graft may be made of a length sufficient to join two blood vessels distant from each other.
However, grafts are associated with a higher rate of thrombosis. The thrombosis may result from stenosis within arteries and veins adjacent to the anastomoses. Grafts are also typically associated with a higher rate of infection than the fistula. Furthermore, like a fistula, a graft cannot be turned “off,” and even after completion of a dialysis procedure, blood is constantly flowing through the graft.
It would be desirable to obtain benefits of a fistula/graft without associated disadvantages. It would be desirable to provide blood access that is associated with a high throughput and that may be “turned off” after a treatment. It would be desirable to provide regular access to blood without damaging a blood vessel as a result of repeated needle pricks. Therefore, it would be desirable to provide apparatus and methods for a hydraulic port for accessing a blood vessel.